High voltage electric cables are typically used for transporting electric power from the transmission network to the primary distribution. A high voltage electric cable can be a submarine cable or an underground cable which connects a power plant site to a primary distribution network.
The voltage associated to the transport of electric power in high voltage systems is typically higher than 35 kV. In addition a high voltage electric cable usually transports a notably high electric current rate.
An electric cable typically comprises a core of conductive material (e.g. copper or aluminium) whose cross section has an area that depends on the electric current rate that the cable must transport. Typically for high voltage applications, the cross section of a cable core has an area ranging between about 400 mm2 and 2500 mm2.
An example of an electric cable used for high voltage applications is the so called “sector cable” disclosed, for example, by U.S. Pat. No. 4,550,559. This document relates to a cable comprising at least one layer of strands with each strand covered with an individual sheath of rubber or plastic material. The sheaths are so shaped that the sheaths of adjacent strands interlock. In particular, the side surfaces of adjacent sheaths are in face-to-face engagement, while the wider surfaces of the strands form continuous cylindrical outer surface to the cable. The cable is made of a sheathed core strand surrounded by six equiangularly spaced strands. Each strand may comprise a plurality (say 200) of cords, each individually surrounded by rubber or similar material.
U.S. Pat. No. 4,175,212 discloses a gas filled high voltage cable in which the inner conductor is constructed from plural elements arranged on a carrier tube in one or several layers. The conductive elements are stranded around the carrier while remaining spaced from each other so that they can deform azimuthally in a wave-like pattern whenever their temperature increases. In particular, the inner conductor is contained in a tubular outer conductor or shield and the space between them is filled with insulative gas. The inner conductor is composed of six segments, e.g. of aluminium or copper. The segments are mounted on top of a tubular support element made, e.g. of metal, that may be a solid tube in which case it may also serve as a conduit for a coolant.